We are synthesizing relatively large amounts of very pure natural and unnatural phospholipids by means of the "Cyclic Enediol Phosphoryl" (CEP) method in order to study the ability of these lipids to form model bilayer membranes (Vesicles). We are studying the aqueous dispersions of the phospholipids by means of electron microscopy, differential scanning calorimetry and 31P nuclear magnetic resonance. We are utilizing the synthetic phospholipids in reconstitution experiments of halobacteria purple membrane. We stress the role of metal ions on the properties of the membranes made from the synthetic phospholipids. The systems being synthesize are: cardiolipin, phosphatidyldiacylglycerol, phosphatidylserine, phosphatidylcholine and certain phosphatidylsterols. The unnatural phosphatidylsterols have the sterol moiety covalently bonded to the phosphatidic acid moiety and include derivatives of cholesterol, cholestadienol, and cholestatrienol. By means of these techniques we are obtaining information on the role of cholesterol in biomembranes. We are also researching the mechanism of energy transduction in the synthesis of adenosine 5'-triphosphate at the inner membrane of mitochondria.